Study On The Control Of A New Dual Three-Level Converter

As an important power electronic equipment,multilevel converter plays an important role in energy conservation,new energy development,electric locomotive traction and so on.With the development of China's industry,the demand for the multilevel converter is also more diversified,and the requirements is also more diverse.Multilevel converter for the transformation of China's industry and the development of new industries will also play a role in promoting.Due to the limitation of the topology and the control method,the effectiveness of traditional multilevel converter is limited.A lot of researches have been done at home and abroad for the improvement of the traditional multilevel converter topology and the development of the new topology.The new dual three-level converter has its unique advantages compared to the traditional multilevel converter,based on which this paper has done a lot of research.Firstly,the topology of the new dual three-level converter is introduced,the working principle and the switching state are analyzed in detail,and the mathematical model of the rectifier side of the new dual three-level converter is determined.Three common modulation strategies are introduced,and the new dual three-level converter adopts the simplified voltage space vector PWM control technology as its modulation strategy,which saves the time of program running.The suspension capacitor pre charging control of the new dual three-level converter is introduced,which can effectively reduce the impact of the current on the topology.Secondly,the problem of the initial control strategy of the new dual three-level converter is improved.The improvement I of control strategy uses the switch redundancy of the rectifier side to adjust the state of the switch,which reduces the area of the uncontrolled area effectively,but the program is more complex in the experimental platform.According to the working conditions of the rectifier side and the inverter side,the improvement II of the control strategy is more reasonable distribution of the duty cycle calculation,which is easy to implement on the experimental platform.Simulation results show the effectiveness of the two improved control method is better.Again,aiming at the problem that power grid side current amplitude fluctuation when the improved control strategy of the dual three-level converter in the regulation of voltage and frequency,the corresponding solutions are put forward.On the one hand,analysis shows that there is no uncontrolled area in the inverter side which operated in VVVF when modulation is satisfied 1-mA_rec?mA_inv,and the uncontrolled area can be reduced by reducing the rectifier side and inverter side modulation when the equation is unsatisfied.On the other hand,it can solve the problem of the grid side current amplitude fluctuation by the method of phase capacitor voltage fluctuation.The correctness and effectiveness of two control methods are verified by simulation analysis.Finally,through the establishment of the experimental platform,the design of the system software,and the debugging on the experimental platform of the improved control strategy,the experimental waveforms are obtained.Through the analysis of the experimental results,it can be seen that the improved control strategy is better to run on the experimental platform.